The semiconductor industry has experienced rapid growth due to continuous improvements in the integration density of a variety of electronic components (e.g., transistors, diodes, resistors, capacitors, etc.). For the most part, this improvement in integration density has come from repeated reductions in minimum feature size, which allows more components to be integrated into a given area. As the demand for even smaller electronic devices has grown recently, there has grown a need for smaller and more creative packaging techniques of semiconductor dies.
An example of these packaging technologies is the Package-on-Package (POP) technology. In a PoP package, a top semiconductor packages is stacked on top of a bottom semiconductor package to allow high level of integration and component density. This high level of integration from PoP technology enables production of semiconductor devices with enhanced functionalities and small footprints on the printed circuit board (PCB). A semiconductor package with a small footprint on PCB is advantageous for small form factor devices such as mobile phones, tablets and digital music players. Another advantage of a PoP package is that it minimizes the length of the conductive paths connecting the interoperating parts within the package. This improves the electrical performance of the semiconductor device, since shorter routing of interconnections between circuits yields faster signal propagation and reduced noise and cross-talk.
Many challenges exist for the manufacturing of PoP packages. For example, due to the mismatch of the coefficient of thermal expansion (CTE) for the different materials used in the package, warpage can occur when the semiconductor package is subjected to repeated heating and cooling cycles during test and normal usage. Serious warpage can cause defects such as cracks and delamination to occur in the semiconductor package. Warpage can also cause unreliable or broken electrical connection between the package and the PCB.
Efforts have been made to address different difficulties for the PoP technology. However, there is still a need in the art for PoP type semiconductor packages which have improved mechanical and/or electrical characteristics.